Many projection systems and other imaging devices incorporate high intensity arc-light sources that have small point sources that are called “fireballs.” The fireball is usually located within a concave reflector that has a focal point, such as a parabolic, elliptical, or other curved shaped mirror. The light emanating from the fireball in the focal point is reflected off the surface of reflector. Often times the reflector is made of a glass, metal, or other substrate that requires a special coating to be applied to provide a specular surface for reflection. When the reflector is fabricated, the special coating may be deposited, sprayed, dipped, painted, or otherwise applied to the reflector surface. For instance, a silver reflective coating may be applied to the reflector to reflect all wavelengths of visible, infra-red (IR), and ultra-violet (UV) radiation.
Often times the light source may need to supply only a limited band of frequencies, such as visible light in video projection systems. For instance, a xenon lamp typically emits about 68% of its emissions in the UV and IR radiation and these unwanted emissions may need to be filtered out. Other applications may only require a band of UV radiation such as in semiconductor lithography. Still other application may just require a band of IR radiation such as with thermal imaging.
Because various applications just require a portion of the light source radiation, typically a “cut” or absorptive filter is placed in the optical path of the light source to absorb the unwanted wavelengths to prevent other optical components from being damaged. Typically this cut filter needs to be cooled effectively to prevent degradation such as clouding which might affect the performance of the desired transmitted radiation.
Accordingly, it would be desirable to have a light source that only provided the desired wavelengths in order to simplify optical and thermal designs in various applications.